Two-stage multiplex switching system employing interlaced connections between highways and external circuit groups



sept. 27, 1966 Filed 001'.. 8. 1965 TOSHlHiRO KUNIHIRO ET AL Two-STAGE MULTIPLEX SWITCHING SYSTEM EMPLOYING INTERLACED CONNECTIONS BETWEEN HIGHWAYS AND EXTERNAL CIRCUIT GROUPS 6 Sheets-Sheet l Sept. 27, 1966 TosHxHlRo KUNlHlRo ET A1. 3,275,749

TWO-STAGE MULTIPLEX SWITCHING SYSTEM EMPLOYING INTERLACED CONNECTIONS BETWEEN HIGHWAYS AND EXTERNAL CIRCUIT GROUPS Sept. 27, 1966 TosHlHlRo KUNlHlRo ET AL 3,275,749

TWO-STAGE MULTIPLEX SWITCHING SYSTEM EMPLOYING INTERLACED CONNECTIONS BETWEEN HIGHWAYS AND EXTERNAL CIRCUIT GROUPS Filed Oct. 8, 1965 6 Sheets-Sheet 3 W w M a W Wc d sept 27, 1956 TosHlHlRo KuNlHlRo ET AL 3,275,749

TWO-STAGE MULTIPLEX SWITCHING SYSTEM EMPLOYING INTERLACED CONNECTIONS BETWEEN HIGHWAYS AND EXTERNAL CIRCUIT GROUPS Filed Oct. 8, 1965 6 Sheets-Sheet 4 Sept- 27, 1966 TosHn-uRo KUNn-uRo ET Al. 3,275,749

TWO-STAGE MULTIPLEX SWITCHNG SYSTEM EMPLOYING INTERLACED CONNECTIONS BETWEEN HIGHWAYS AND EXTERNAL CIRCUIT GROUPS Filed oct. e, 1965 e sheets-sheet 5 MfS/140,? y

Sept. 27, 1966.` TosHn-nRo KUNu-nRo ET AL 3,275,749

TWO-STAGE MULTIPLEX SWITCHING SYSTEM EMPLOYING INTERLACED CONNECTIONS BETWEEN HIGHWAYS AND EXTERNAL CIRCUIT GROUPS 6 Sheets-Sheet e Filed Oct. 8, 1965 United States Patent O M Japan Filed Oct. 8, 1965, Ser. No. 494,221 Claims priority, application Japan, Oct. 14, 1961, 36/ 37,202 6 Claims. (Cl. 179-15) This invention relates to switching systems and more particularly to a nofvel arrangement for ltwo-stage multiplex switching systems which is adapted to provide a plurality of alternate paths for message transmission so as to overcome blocking due Ito troubled lines and which is further adapted to perform these functions without the necessity for adding duplicate equipment to perform such functions, and is .a continuation-in-part of copending application Serial No. 230,138, led October 12, 1962, entitled l`wo-Stage Multiplex Switching System Employing Interl-aced Connections Between Highways and External Circuit Groups.

In multiplex switching systems such las, for example, time-division multiplex switching systems, subscriber lines at remote locations are normally connected to predetermined trunk lines. Interconnections between these trunk lines are affected automatically upon identification of the called subscribers identifying number so as to appropriately interconnect the called to the calling party. In order that ya plurality of subscribers which may be connected to each such trunk line may be aiforded continuous service, -it is well known to multiplex messages on each trunk line wherein each Isuch subscriber is afforded a specific time slot during which the subscribers message is carried through the network. In such systems,fif the trunk line to which a plurality of subscribers are connected becomes out of order, this situation thereby disables all of the subscribers connected to that trunk line. It is therefore incumbent upon the network to provide some :alternate means of service for the affected subscribers in order that service may continue during the time period in which the disabled trunk line is being repaired or replaced.

One manner of carrying this out is to provide .an alternate, or standby, trunk line for each existing trunk line in the network which may be automatically substituted into the network in place of the disabled trunk line so that subscriber service may continue throughout the repair or replacement period. As can clearly be seen, such a system requires a substantial duplication of already exitsing equipment producing in effect two identical networks, one being the standby network and the other being the existing network, which is normally employed unless and until some disorder occurs, at which time a trunk line or trunk lines of the standby network may be substituted in place of the disabled trunk lines. While it is necessary to provide some means for maintaining service, in spite of disorders which may occur through operating periods, the above mentioned -solution becomes a rather costly one from the viewpoint of equipment expense. Y

The instant invention overcomes the disadvantages of a single network system having no alternative paths by providing alternative paths which may be employed during times at which a disorder may occur and further, requires substantially no increase in the network size and hardware, to perform these functions. In addition thereto, the system of the instant invention provides a 3,275,749 Patented Sept. 27, 1966 ICC plurality of alternate paths as opposed to a single alternate path which may be employed during a time at which some trunk line has become disabled.

The instant invention is comprised of a two-stage multiplex switching system having a plurality of subscriber groups wherein each subscriber group has la plurality of subscribers within the group which are multiplexed to a trunk line in any suitable fashion, such as, for example, by means of a time-division multiplex arrangemnt Neighboring subscriber` groups Iare interconnected to a cornmon trunk line forming a closed loop arrangement such that no more than two neighboring subscriber ygroups have no more than one common trunk line. This arrangement, coupled with the time-division multiplexing control circuitry, acts to provide a plurality of alternative paths through which a message may be transmitted so that upon the occurrence of a disorder in any trunk line of the system, any one of the alternative paths may be selected so as to route messages being transmitted without the necessity for waiting until the disabled line is placed back into service.

In order to provide still more flexibility, the tim division multiplx switching systems, which interconnect trunk lines of each group, are arranged so as to provide interconnections within line groups (wherein eachtrunk line group has a plurality of individual trunk lines comprising the group) in the switching network so as to provide a greater variety of alternate paths through which messages may be routed if any of lthe existing lines bec-ome disabled.

It is therefore one object of this infvention to provide a multiplex switching system having a novel larrangement for providing alternative message routes which may be employed if a preferred route is disabled for any reason.

Another object of this invention is to provide la multiplex switching system which is adapted to transmit subscriber messages through alternate routes due to the disabling of a preferred route wherein connections are provided for each subscriber group to share a common trunk line with a neighboring group.

Still another object of this invention is to provide a multiplex switching system having switching arrangements for interconnecting trunk lines in such a manner las to have neighboring trunk lines share .a common trunk line for the provision -of alternative message groups.

These and other objects of the invention will become apparent when reading the accompanying description and drawings in which:

FIGURE l is a schematic trunking block diagram of a 'conventional two-stage time division multiplex switching network.

FIGURE 2 is a schematic block diagram showing a portion of the network of FIGURE l in greater detail. FIGURE 3 is a schematic trunking block diagram oi a conventional duplicated two-stage time-division multiplex switching network.

FIGURE 4 is a block diagram showing a portion ol the subscriber network of the system of FIGURE 3 in greater detail.

FIGUR-E 5 is a trunking block diagram of a two-stage time-division multiplex switching system designed in ac cordance with the principles of the instant invention.

FIGURES 6, 6a and 6b show a portion of the subscribe; network of the system of FIGURE 5 in greater detail.

FIGURE 7 is a trunking block diagram of a three-stag multiplex switching network designed in accordance'witl the principles of the present invention.

FIGURE 8 isa block diagram showin-g a portion of th( subscriber circuit of one subscriber group of FIGURE i in greater detail.

Among the many advantages of multiplex switchin; systems, one salient feature is that of the reduction in tht 3 number of physical elements required in the multiplex arangement, asl compared with a space-division switching ietwork, such that the multiplex arrangement is elfected Jy multiplexing switches contained within la switching netvork on a time-division, or a frequency-division basis. ,TIGURE 1 shows one such time-division switching system 100 which comprises five time-division common busses hereandafter referred to as highways), H1, H2, H3, H1, md H5 and tive subscriber vand/or trunk groups (hereuafter referred to as subscriber groups), S1-S5 wherein he subscripts for the subscriber groups S conform respecively to Ithose subscripts for the highways H. Between my two highways, an interconnecting link, such as the inks L12, L13 L23, L24 L15 containing a set of imc-division contacts such as the contacts 101-104 is rrovided. These interconnecting links L are used for the imc-divisional connection of calls between subscribers which pass through two dilerent highways H, and conrolled by cyclic memories (not shown). FIGURE 2 hows a circuit diagram 200 illustratingk more detailed onnections between the individual subscribers of sub- V `hese Switches may, for example, be well-'known diode 1 uads which are controlled by a distributor Distributor, 'hich is in turn controlled by a C switch gating memory GM. CGM is a cyclic memory for storing the address iformation `of the time-divisionswitches C which are y be gated atthe specied time slot. The number of 1e words stored in the cyclic memory CGM is equal to le' number'of` time -slots which will be explained later. he addressA yinformation is fed into the Distributor 'hich decodeszthe information vand gates the laddressed vitch for each :time slot. The central control can 'aange the contents of any time slot of any CGM. It 1ould be .understood that each of the remaining sub- :riber groups S2-S5 shown in FIGURE l, in a like maner, are comprised of a plurality of individual subscribers 'hich are connected by multiplexing switches to one comlon highway lin a manner similar to that shown for the ibscriber group S1 of FIGURE 2.

Referring to FIGURES 1 and 2let; it be assumed that connection isto be made 'between subscriber S11 in the rbscriber group S1 and subscriber S32 in subscriber group 1. In order that this interconnection be completed, it is :cessary that all time-division switches contained in the Clt Ute S11, C11, H1, x [143], HsrCaz (Ilot Shown), Saz (x Y enotes the time-division kswitch 101 in Vinterconnecting uk L13 between highways H1and H3), be switched ON lring a short time interval t (hereinafter referred toas time-slot t1) within` a constant time period T atV which ne all switches in the aforementioned message loop are med ON (i.e., closed) for an interval t and OFF for the l Forkclarity ,and simplicity of the explanation set forth ythis disclosure, details of the highways H1 (where i is ual to 1-15), the time-division contacts 101-104 and bscriber circuits and trunks S11 are not illustrated in del in FIGURE 1.- It should `be understood, however, at in the case of a four-wire system,-both highways and rie-division contacts should be duplicated, one for transtter` side and the other for vthe receiver. side, whereas in a 'case of a two-wire system, highways and time-division contacts shown in the block diagram correspond respectively, to H1 and 101-104. The modulation systems em-` :as shown in FIGURE 2. The general operations of such time-division switching lsystems are known to the prior art and for this reason a detailed description is omitted here for the sake of brevity since the invention isspecically concerned with the trunking scheme. The central' con-l troller 301 is lprovided with suitable means (not shown) for monitoring all of the subscriber telephone handsets within the system to determine their state (i.e., in use, or not in use)Y at any given instant and alsoto determine that time slot which the subscribers on line may be using .at any given instant. One systemwhich may be employed to determine the state of all the telephone subscribers in the system is set forth in detail in copending U.S. `application Serial No. 211,962, entitled 1Automatic Telephone 1 Switching System, tiled July 24, 19,62, and assigned t0` l the assignee of the instant invention. This system basically has the capability of monitoring all subscribersrwithin the system by continuously scanning all ofthe subscriber lines 1 and providing an indication of the stateof each line'rbeing sensed, together with an appropriate identifying code` for each line, as well as an indication of the` time-slot which any given subscribermay be using.,k

Another system which, may be employed `for use1in determining the state of each subscriber line and the t time-slot which on-line subscribers may be utilizing at any given instant is set forth in copending U.S. application Ser-ial No.; 441,980, entitled Variable Sampling Rate Time-Division TelephoneExchange System, filed March 23, 1965, and assigned yto the assignee ofthe instant inz vention. In this application means are providedfor opf` erating the switching means'for connecting the called to` the calling subscriber, storing this `information in suit-i able memory means and means to compare new requests for calls against the lines .and-.time-slots presently inv use in order toY determine `which time-slots :andlines are available for establishing `connections between gparties presently requesting that -a call'be connected.

The central controller -201feeds informationinto the switch gating memories CGMl-CGMS y.which is indicative of .the available time-slot together withan indication of the calling (or called) party which is being designated that. particular time-slot..l The` memory,.for example,

may be a rotating drum memory with each genetrix con-i taining all the available time-slots t Within the time period '-I` for thetotal number of time-slots available is equal to T-z-t. During la time duration T t in'which the` subscribed S11 is-not connected to its called party4 thel Dis- 1 tributor1 .doesl 4,not receive the .code identifyingj sub-k scriber` S11 and its allocated time-slot and impressesA a rlarge voltage acrossthe terminals 206 and 207 with terminal 207 being positive relative to terminal 206;` The polarity of the diodesl202-205etectively .establishes a .short-circuit between these terminals, preventing S11 from Vbeing connected to highway H1. During the time-slot in which S11 isto be connected to highway H1 this, voltage` i is-removed, permitting S11 to be coupled to highway H1.

V,In a likeY manner, the cyclic memory CGM3 (not shown 4 in FIGURE 2) operates to couple subscriber S32 (not shown in FIGURE 2) to its highway H3 in order to cou ple the subscribers .to theirrespective highways. In a likel manner, another cyclic memory and 'distributor means 1 (not shown in FIGUREZ) is provided for the purpose. of. coupling the Highways H1 and H3 to complete the connection between subscribers S11 and S32. This arrangement may take the form of a cyclic memory HGM1 which operates a distributor to control a diode quad arrangement for coupling highway H1 to H2, in the manner shown in FIGURE 2, wherein the cyclic memory HGM1 is also under control of the central;controller 201. A similar cyclic memory and distributor is provided for connecting each of the other highways t-o one another with the number of cyclic memories HGM1 and their associated distributors being equal in number to the highway connections made. For example, considering FIGURE l which teaches the -use of ve highways for tive subscriber groups, the total number of combinations of connections between highways is ten and hence ten cyclical memories and associated distributors would be required to establish the necessary highway interconnections.

Referring again to the network of FIGURE 1, it will be understood that the number of subscribers, or that of trunks in the S1 group (i being any number l-5) which belong to a highway, may be any predetermined number, such as 100 or 1000, which depend upon the number of time slots available in thertime period T on the associated highway H1 and the amount of traliic. Upon the occurrence of a disorder in any highway or in any common circuitry in a subscriber group the highway becomes iuoperative.l T-he manner in which a system copes with such a situation becomes invariably a problem of how to establish a countermeasure in a system as illustrated in which a subscriber group is assigned to a single highway equipment facil-ity. This is the reason why many systems have gone to the provision of at least one standby unit which may be one which operates in parallel with the operational unit at all times or may be one which operates only in the case of occurrence of a disorder, in order to prevent the termination of operation of subscriber units in subscriber groups from developing into a critical problem in the entire system or in a comparatively large portion of the entire system.

One common method that has been employed in the past and has been reduced to practice for meet-ing the situation of a disablement in the system, consists in the duplication of all highway components `and common circuitry in each subscriber group. In such a case, all time-division contacts, such as Ithe contacts 101-104, switch C11 connecting subscribers S11 to highways H1 and time-slot storing devices CGM1, and so forth, will have to be duplicated.

Such an arrangement is illustrated by the system 300 of FIGURE 3. As illustrated therein, each subscriber circuit, or each trunk, corresponds to two independent time-division switching networks through two dilerent sets of time-division contacts. FIGURE 4 illustrates a portion 400 of the network showing the detailed connections between the subscribers S11- and the operational and alternate highways H3 and H1', respectively. It can therefore be seen from FIGURE 3.that the system 300 is comprised of a purality of subscriber groups S155 and each subscriber group is provided with an operational and a duplicate, or alternate highway (H1-H5 and H1H5', respectively. This arrangement enables each such subscriber group, if one of its highways or common circuitry in the subscriber group becomes inoperative, to avail itself of the alternate highway, which is identified by the primed group. The subscriber group 400 for S1 shown in FIGURE 4, shows the interconnections between each individual subscriber S11-S1n to the operational and alternate highways H1 and H1' by Vmeans of C11 to C111, and C11 to C111, or CGM and CGM or Distributor to Distributor. lIt can therefore be seen that double the number of components are required in order to provide the protection necessary to prevent network down-time due to a disablement of any highways H within the network 300.

FIGURE 5 illustrates the composition of a time-division switching network in accordance with the instant invention. In the composition of the network 500, shown in FIGURE 5, it will clearly be shown through the ensuing description that no duplication of circuitry need be performed for the highways H1-H5 and the highway interconnections or links L11, thereby substantially differing from the arrangement shown in FIGURE 3, with the eX- ception that two sets of time-division switches are provided for connecting each subscriber unit or each trunk to two highways. Thus, each S1 (subscriber) group where i is equal to any number Eof 1-5, is interconnected to two diierent Hfs (i.e., highways). That is, each S1 group of the network 500 is interconnected to at least two adjacent highways, H1and Hk -where k is equal to i minus. lf k is zero, it should be understood as 5. In the case where two or more S1fgroups should correspond to the same two H1 sets, correspondence shifts with the subscript by one in a successive arrangement, then looking into the system from one such highway H1, two S1s are connected thereto and in no case are the same two S1s interconnected with another highway H1. That is, in no case are the two neighboring subscriber groups S1 interconnected t-o two common highways H1. If `the combination correspondence is determined by transferring subscript numbers in successi-on iri a cyclic order in `such a manner that:

S1 is related to H5 and H1; S2 is related to H1 and H2; S5 is related to H4 and H5. The above mentioned correspondence can `be realized among equal numbers of subscriber groups S1 and highways H1 of three or more. FIGURE 6 shows this arrangement in greater detail. Now comparing FIGURES 2 or 4 with FIGURE 6, the com-mon circuitry of a subscriber group in FIGURE 2 or 4, such as CGM and Distributor, is no longer common to a single subscriber group in FIGURE 6. The common circuitry in FIGURE 6 is shared by two neighboring subscriber groups which are connected .to a highway. Therefore, the word highway is hereafter used in what is defined to be a novel sense. The highway is comprised of accessories such as CGM and Distributor and receives multiplexed messages which are transmitted in a time-divisional way. The operation oi the cyclic memories and distributors for coupling the subscribers to their respective highways and for connecting respective highways is substantially identical to that described with respect to FIGURE 2. The major distinction between the arrangement of FIGURE 2 and FIG- URES 5 and 6 is that each of the subscribers of a single subscriber group such yas, for example, the subscribers S11-S1n of subscriber group S1, 'are coupled to a pair o1 highways H1 and H5. Arrangement, in its simplest form, is shown best in FIGURE 5. The detailed arrangement of the subscriber groups S1, S2, S4 and S5 is shown in FIG- URES 6a and 6b with the subscriber group S5 being omitted only for purposes of clarity and simplification. B5 controlling the cyclic memories and associated distributors for 'both subscriber switch connections and highway switch connections in the same manner as previously described with respect to FIGURE 2, connections betweer subscribers of different subscriber groups may be made In the case where one of the two highways coupled witl each subscriber group is unavailable during all time-slotf tl of the time period T, the remaining of the two highway: associated with that subscriber group may be used as a1 alternative circuit path to provide the appropriate connection between calling and called parties. For exam ple, considering subscriber S11 in subscriber group S1, this subscriber is coupled through the switch C11' (which i: comprised of a diode quad) to highway H5. Subscriber S11 is also connected in common through switch C1; (which is also comprised of a diode quad) to highwa H1. In order to connect subscriber S11 to highway H5 distributor5, under control of cyclic memory CGM5, an( the central controller removes the bias from the diode quad C11 to establish a connection from S11 to highwag H5. Simultaneously therewith the central controller op erates cyclic memory CGM1 land its associated Dis tributor1 to operate diode quad C11 to prevent a con nection from S11 to highway H5. The alternative opera 7j on may likewise be provided in order to inhibit connecon yof S11 tohighway H5 and to establish connection ,'omS11 to H1. The alternative pairs of highways H2 nd H3 are Aavailable to subscriber group S3 land the final ighway selected (H1 or H5 in the case of subscriber S11 nd H2 or H3 in the case of subscriber S32) are coupled trough suitable vcyclical memory means and distributor leans to connect the 4appropriate highways to which the lscribers have been connected in order to complete the annection between calling and called parties. In the /stem 400 shown in FIGURE 4 which represents conentional practice in tirne-division multiplex systems each ibscriber lgroup `such as, for example, the subscriber roup S1 is connected to a pair of highways H1 and H1' nd requires a separate cyclic memory'and associated dis- 'ibutor for each highway coupled to the subscriber` group. 1 the example of FIGURE 4 for tive separate subscriber roups S1-S5 this -arrangement requires ten highways H1-H5 and H1f-H5) as compared to the system of IGURES `5, 6a and 6b which requires only tive high- 'ays. The system of FIGURE` 4 thereby requires ten Iclic memories and associated distributor circuits for ecting all of the connections to the alternative highway foups with a total of 45 combinations of connections :tween the highways H1-H5 and group H1-H5. In the rangement of the instant invention shown in FIGURES z and 6b, lone cyclic memory and its associated disibutor may be shared by two adjacent subscriber groups.l

distributors and cyclic memories are required for ther :vel system of FIGURES 6a and 6b in order to estabih connections between individual subscribers within .bscriber igroups and their associated highways. The tal number of possible combinations between highways lr the embodiment of FIGURES 5 1and 6a and 6b is only n compared with 45 possible combinations with the sysrn 400 of FIGURE 4 which depicts conventional pracze. It can therefore be seen that the arrangement of e instant invention in which adjacent subscriber groups ,are a common highway or conversely where each subriber group is coupled to -a pair of highways that the lntrol circuits are much fewer in number than the con- )l circuits required in the system of FIGURE 4. It ould be noticed that this definition will not be confused th the previous description since in the prior art system td the systems referred to hereinabove with reference to GURES 2 and 4 there is one-to-one correspondence be- 'een a subscriber group, common circuitry of a subriber group, and a highway. When the number of sub- 8 system of FIGURE 5 isrelatively small according to the principles of the instant invention.

(2) The number of connection routes between two different subscriber groups S1, such as, for example, between the subscriber groups S2 and S5wil1 =be as follows:

In the case of FIGURE 3:

As can 'be seen from the above development of the existing paths between subscriber-` groups, the arrangements of FIGURES 3 and 5,'the number of 'available routes according to the instant invention system, -and the con-` ventional system, are respectively, 4 and 2.1 Therefore, in the case of occurrence of a trouble condition in a high- Y way, two routes still exist according to the instant invention, whereas 'according to the conventional1system, only one route is still in operation. Thus, the present'inven-` tion oiers higher communication reliability. As viewed reduce the line blocking rate. Thus, the system designed in accordance with the principles of the instant invention has a larger call carrying capability than that of the conventional system. While the call carrying capabiliti of` from a traliic viewpoint, a large number offroutes help i ently `of each other and also when no trouble exists on.

the line. On the other hand, however, the trattic load to the full extent of the effective number of links capable of use in trouble-free condition can never be lapplied to theV system of FIGURE 3 when the grade of service under aA the system `as shown in FIGURE 3.

riber groups S1 and highway H1is two, the correspondce takes a degenerated form such that subscriber group is related to highways H1 and H2; subscriber group two related to highways H1 and H21 such that highways H1 `d H2 correspond to `both subscriber groups S1 and S2 can be seen therefrom. Y FIGURE 6 Ashows the. manner in which subscribers 1-S1n`of subscriber group S1 (for example) are concted to highways H1 and H5 in multiplex fashion rough switches C11-C1x1 and C11-C1`11V respectively.

In the case where the number of both subscribery groups and highways H1 is three, or greater, the comparison the network composition 300 'of FIGURE 3 and the twork composition 500 of FIGURE 5 readily reveals e following advantages of the instant invention over nventional methods: Y 1 f Y (1) With the conventional network composition 300` FIGURE 3 all units inclusive of time slot stores with a exception'of theindividual subscriber circuits S15 have service for the connection which should have been ,used` for said other routes is sacrificed to a certain'extent.

However, Vconsidering calls using said other routes which" are free from trouble calls using the disabled route and those whose calling and called subscriber 'groupsY S1 are` diierent, it can readily be transferred through a number of other trouble-free routes.

' In the` case of the system designed in accordance4 with the instant invention, .the number of routes in the absence of trouble isy large with the result that the deleterious effect due to abnormal traic that cannot be passed through ya trouble route or routes and ows. into -side routes may be dispersed and mitigated over the numerous remaining routes. Inl contrast, when la network consisting of highways H1 (i iscqual to l-5)` and the networkconsisting Y lof alternate highways H1f (i is equal to l-5)`,as shown in i FIGURE 3,' operaterindepenfdently'of one another, the inuence of all trouble in highway H1 becomes concen- Itrated in the alternate highway H1 to 'appear as an `ini crease in'traiic resulting in `a lange decrease .in the grade of service upon the occurrence of trouble in Vthe `line H1. It should be understood that the. time-slot generating fa,-

cilities and their accessories for controlling ,thetime-r division contacts for that part` of the highway network which has not been duplicated in this invention, should be suitably decentralized with respect to the associated highway members. Since the time-slotA facilities mentioned above contain a small quantity of infomation data, the advantage of centralizing this ydata in one unit which corresponds to the entire network can be disregarded when viewed from the benefits derived in accordance with the instant invention.

Where the number of subscriber groups S1 and highways H1 is two, a part of the advantages of the system vaccording to the instant invention as mentioned previously cannot be realized. The features of the invention are nevertheless still retained.

As recited previously, a comparison has been set forth 4between the embodiment of FIGURE 5 and the Vconventional system shown in FIGURE 3. As will be evident from this description, the two-stage multiplex switching system provides a system in which the duplicated fpart of the common circuit is optimally minimized. A decrease in the grade of service in the case of troubled condition is minimized and the condition for the link blocking rate in normal operation has been substantially improved and hence the` overall call carrying capabilities have been enhanced.

Referring now to FIGURE 7, a switching network l700 is shown therein which is comprised of a plurality of subscriber groups S11-S13-S51-S53 which are directly associated with highway groups H11-H13-H51-H53, respectively. S11- contains a plurality of individual subscribers within the group. The highways H11- are electrically connected by means of the interconnecting links Hg wherein the interconnections between highways are represented by the circles 701-705 which surround the crossing lines at their intersections. The highway group H21 is interconnected to the subscriber groups S11 by means of the interconnecting lines 707 shown as the dot-dash lines in FIGURE 7. This pattern is repeated throughout FIGURE 7 with respect to all remaining highways and the subscriber groups and as can be noted, the interconnecting lines 7061 have been repeated at both the upper and lower portions of the figure so as to represent a closed loop of such interconnecting Ilines wherein all such interconnecting lines 706-710 are shown in dotted fashion. For the purpose of describing the operation of the circuit of FIGURE 7, let it rst be assumed that the interconnecting routes 706-710 have been removed. Then the network remaining is .nothing more than the conventional multiplex switching system. Now

let it be required to provide a description of a con-' ventional multiplex switching network for the case of a time-division system.

Assuming therefore that the interconnecting routes 706-710A represented by the dot-dash lines have been removed, then timedivision highways H11, H12, H13,

H53 correspond and are connected respectively with the subscriber trunk groups S'11, 5'12, S13, in the arrangement of FIGURE 7. The manner in which subscriber group S32 is connected to highway H32, for example, is shown in greater detail in the arrangement 800 of FIGURE 8 where the subscriber group S32 is comprised of Ia plurality of individual subscribers S321-S3211. All of the subscribers S321-S32n in subscriber group S32 are connected to the highway H32 by the time-division switches 801. In FIGURE 7 it should be noted that the highways having the same rst subscript are grouped together such as, for example (H11, H12, H13); (H21, H22, H23) (H51, H52, H53). Each of these groups shown in parenthesis will be referred to as highway groups hereinafter in the ensuing description. In addition to the above the intergroup highways H212 Hgra, Hg43, are provided for interconnecting the highway groups to one another. The highway groups will be identified on a group basis, as shown in FIGURE 7 by GH1, GH2,

GH5. In addition to the above intragroup highways Hgu, H322, H355 (not all of these have the 10 same subscripts), are provided for connection within each highway group GH1-GH5, respectively, by the use of the time-division contacts 701-705, respectively.

Each intragroup highway connection is therefore represented by a circle encircling the intersection between the connecting link and the highway lines in the same manner as previously described with respect to the contact connection 701-705.

Let it now be Kassumed that S121 of the subscriber group S12 is to be connected with the subscriber S312 of the subscriber group S31. It should be understood that the route between the subscribers S121 and S312 is formed through the subscriber S121, the contact for connecting the subscriber S121 to highway H12 (see, for example, the contact 801 of FIGURE 8), H12, contact 701', H313, contact 703', H31 and the Contact connecting the subscriber S312 to H31 (see the contacts 801 of FIGURE 8) and ultimately subscriber S312. Thus, with such a connection it is only necessary that all of the time-division switches (which control the abovementioned four contacts, respectively) contained in this route are t-urned ON sim-ultaneously within the time interval t of the time-slot t1, as it is more generally called, which time interval t is repeated after a predetermined time period, T. Simultaneously therewith, different connections can be established using the time slots each differing in phase from the time slot t on the'highways and the intergroup highway H12, H31, and H213. On each highway and each intergroup highway the same number of connections as the maximum number of time slots within the time period T can be handled at the same time. The aforementioned features of the multiplex switching system are thus realized in this manner.

The foregoing description has been for the case in which connection routes 706-710, shown by the dotdas-h lines are absent from the circuit 700. The nurnber of subscribers and/or trunks contained in each subscriber group S11 belonging to each highway may be on the order from to 1000, for example, and are decided primarily by the number of time-slots and the amount of traflic on the highway under consideration. Upon the -occurrence of a troubled condition on one highway, or within the highway accessory equipment, all of the subscribers S11 belonging to the effected highway therefore become inoperative. In addition thereto, it will readily be seen that a trouble on one intergroup highway effects all of the traflc on said intergroup highway or upon the intragroup highway. Such a defect presents quite a troublesome problem invariably in systems in which one function is assigned to a single piece of physical equipment. This is the reason why the provision is made of at least one standby facility (which may be operated in parallel with the operational facility at certain times, or may be operated only in the case of an emergency), so that a troubled condition in one functioning unit may not develop into a critical problem Vfor the entire system or for an appreciably large part of the entire system.

With respect to the aforementioned intergroup highways H211-, it has been assumed that Kprovision be made of one intergroup highway between each two highway groups, but it may be advisable from the traic viewpoint to provide a plurality of intergroup highways at specified times. Since this stage is a switching stage in which concentration has been effected, the number of highway group combinations is essentially reduced so that it is not diicult to provide a plurality of intergroup highways at all times. Although it has been assumed in the foregoing description that the number of routes from each individual subscriber S151i is one, let a method be proposed for making the number of routes greater than one.

Among ythe features of the instant invention is to connect each individual subscriber S113 through the appropriate time-division Contact sets to a highway in a highway group -Which is different from fthe highway group i :o which the individual subscriber is :already connected. l`his is illustrated in FIGURE 7 by Vthe provision of the :lot-dash line groups 706-710 which provide the aforenentioned connections. This is also shown in greater ietail in FIGURE 8, which depicts one subscriber such as subscriber S322, for example, which is connected to aighway H32 via one of a plurality of time-division con- :acts 801, and 'which is further shown as being connected :o highway H42 via one of a plurality of time-division :ontacts 801'. In this manner, homogeneous and cyclic :onnections can then be secured in the entire highway ietwork. The advantages of this arrangement are as follows:

(l) The switching network (including the time-slot nemories as well), at stages subsequent to the time-di- /ision switches for direct connection to the subscribers S151; are not duplicated, resulting in a substantial decrease n the number of equipment facilities required in the renaining portion of the network.

(2) Considering the number of routes extending beween subscriber S121 and S312; S121-Contact 121 (not ihown; corresponding to contact 801 in FIGURE 8) asigned toS121-H12-Contact 701+Hg13-Contact 70E/ H21- ontact 312 (not shown; corresponding to Contact 801 n FIGURE 8)-S312;

S121 Contact 121-H12-701Hg14-Contact 704-Hg44 '.ine 7091-Contact 312` (not shown; corresponding to :ontact 801 in FIGURE 8) S312;

S121-Contact 121 (not shown; corresponding to conact 801 in FIGURE 8)-Line'7072-H22-702'Hg23703 {3l-Contact S12-S312;

Thus, from the above described routes, it can be seen hat if any highway becomes faulty, at least two remain, vhich are free .from any trouble. Viewed from a traflic tandpoint, numerous routes are definitely advantageous n reducing the link blocking rate and in enhancing the :all carrying capabilities. Assuming for a moment the low of traic in the case of trouble is constant in each iighwvay, in such a case it is evident that the calls `that hould have `been carried over-'these routes must be caried over other routes. Thus,` of calls that should have 'een carried over said other routes, if'no Vtrouble has lccurred, that part of the calls whose originating and/ ir destination subscribers were dilerent prior to the ocurrence ofthe trouble from the ones which should .ave been carried over said routes, can be transferred 1e deleterious effects therefrom are substantially re-V eved.

While the principles of the instant invention have been escribed above in connection with a specific embodiient, the description is made by way of example only nd not as a limitation to the scope yof the instant inention. For example, modifications of the number of ighways and intergroup highways, or the number of ibscriber groups and/or trunk groups, or of interconections of trunk groups at each stage or stages other 1an the subscriber stage, this circuits system should pre- :nt no restriction to the scope of the system in accordnce with the instant invention. Two modes of embodif lents of the instant invention are the modes of FIG- lRES 5 and 7 which set forththe network of link ciriit stages of two and three stages respectively. It should irther be understood that differences within the system, ich as time-division and frequency-division systems, or

1 the -number of highways or in the number of sub- :riber trunk groups, or lthe dilerence in partial circuit 12 systems, are intrinsic with the yspirit of this invention and hence in no way restrict the scope of the system accord' ing to the instant invention.

Although there has been'described a preferred embodiment of this ,novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, thisl invention is to be limited, not by the specic disclosure herein, but onlyl by the append-1 ing claims.-

Y What is claimed is:

1. In a time-division multiplex switching network comprising a plurality of subscriber groups and a plurality of highway lines equal in number to said plurality of-sub` scriber groups, a plurality rof first multiplex switching` means for connecting the subscribers of each subscriber Y group to a first end of their associated highways on a time sharing basis; a plurality of second multiplex switching means for interconnecting the highways of they dif-` ferent subscriber groups at a location removed from the first ends of'said highways in accordance with `the selection of a called subscriber kby a calling subscriber;

said second multiplex switchingrneans being operative on a time sharing basis;means for connectingpairs of said subscriber groups to` a common highway through selected ones of said first multiplex switch means wherein a different highway is connected to` eachpair of sub-` of highway lines associated with said groups, a plurality of first multiplex switching means for `connecting the subscribers of each subscriber group to a lirst end of their associated highways on a time-division basis;` a plurality of secondmultiplex switching means for interconnecting the highways of the difieren-t subscriber; groups I. at a location removed from the iirst ends of said highways i 1 in accordance with the selection of a called subscriber` by a calling subscriber; said second multiplex: switching p means being operative on a'time-division basis; means for connecting pairs of said subscriber. groups to a common highway through selected ones of said first multiplex switching means wherein a different highway is connected 1 to each pair of subscriber. groups and `no more .thancne' highway is `directly associated with any one pairof subscriber groups said second multiplex switchingmeans comprising a plurality of means for selectively connecting said highways on a time-division basis; each of said plurality of means connected between no more than two of said pluralityk of highways. Y

3. A Itime-division multiplex switching network comprising at least lthree subscriber groups, each of said groups including .a plurality p of :individual subscribers; 1 at least three highways, each `of said highways Ibeing 1 associated with no more than vtwo of said subscriber groups; rst multiplex switching `means for each of said subscriber groups'for connecting-the subscribers of the group to a irst end of'their associated highway onY a time-division basis; second multiplex switching means for interconnecting the highways of the network at a location removed from the iirst ends of said highways in` accord-f operative on a time-division basis; means for connecting pairs of said subscriber groups to ,a common 4highway through selected ones of said first multiplex switching means AwhereinV no lmore than two of said subscriber groups are connected to more than one of said highways said second multiplex switching means comprising a plurality of means for selectively connecting said highways on a time-division basis; each of said plurality of means connected between no more than two of said plurality of highways.

4. In a switching network comprising a plurality of subscriber groups and a plurality of highways associated with said groups, a plurality of lirst multiplex switching means for connecting the subscribers of each subscriber group to a lirst end of their associated highways on a message sharing basis; a plurality of second multiplex switching means for interconnecting the highways of the different subscriber groups at a location removed from the first ends of said highways in accordance with the selection of a called subscriber by a calling subscriber; said second multiplex switching means being operative on a message sharing basis; means for connecting pairs of said subscriber groups to a common highway through selected ones of said first multiplex switching means wherein a dilerent highway is connected to each pair of subscriber groups and no more than one highway is directly associated with any one pair of subscriber groups, each of said highways comprising a plurality of highway lines forming Va highway line group; third multiplex switching means for interconnecting between and among the highway lines of each highway line group.

5. A time-division multiplex switching network comprising at least three subscriber groups, each of said groups including a plurality of individual subscribers; a plurality of highways equal in number to said subscriber groups, each of said highways being associated with two of said subscriber groups; rst multiplex switching means for each of said subscriber groups for connecting the subscribers of the group to a iirst end of their associated highway on a time sharing basis; second multiplex switching means for interconnecting the highways of the network at a location removed from the first ends of said highways in accordance with the selection of a called subscriber by a calling subscriber, said second multiplex switching means being operative on a time sharing basis; means for connecting pairs of said subscriber groups to a common highway link through selected ones of said rst multiplex switching means wherein no more than two of said subscriber groups are connected to each of saidhighways, each of said highways comprising a plurality of highway lines forming a highway line group; third multiplex switching means for interconnecting between and among the highway line of each highway line group said second multiplex switching means comprising a plurality of means for selectively connecting said highways on a time-division basis; each of said plurality of means connected between no more than two of said plurality of highways.

6. A time-division multiplex switching network lcomprising a plurality of subscriber groups, each of said subscriber groups including a plurality of individual subscribers; a plurality of highways, equal in number to the number of said subscriber groups; said subscriber groups being arranged in pairs; said pairs of subscriber groups being associated with a common highway wherein the rst end of a different highway is connected to each pair of subscriber groups and no more than one highway is directly associated with any one pair of subscriber groups; a plurality of rst multiplex switching means for connecting each of said individual subscribers to the highways associated to the subscriber group including each of said individual subscribers on a time sharing basis; a plurality of second multiplex switching means for interconnecting said highways at a location removed from the first ends of said highways on a time sharing basis; at least one of said rst and said second multiplex switching means being operative in accordance with the selection of a called subscriber by a calling subscriber said second multiplex switching means comprising a plurality of means for selectively connecting said highways on a time-division basis; each of said plurality of means connected between no more than two of said plurality of highways.

No references cited.

DAVID G. REDINBAUGH, Primary Examiner.

I. MCHUGH, Assistant Examiner. 

1. IN A TIME-DIVISION MULTIPLEX SWITCHING NETWORK COMPRISING A PLURALITY OF SUBSCRIBER GROUPS AND A PLURALITY OF HIGHWAY LINES EQUAL IN NUMBER TO SAID PLURALITY OF SUBSCRIBER GROUPS, A PLURALITY OF FIRST MULTIPLEX SWITCHING MEANS FOR CONNECTING THE SUBSCRIBERS OF EACH SUBSCRIBER GROUP TO A FIRST END OF THEIR ASSOCIATED HIGHWAYS ON A TIME SHARING BASIS; A PLURALITY OF SECOND MULTIPLEX SWITCHING MEANS FOR INTERCONNECING THE HIGHWAYS OF THE DIFFERENT SUBSCRIBERS GROUPS AT A LOCATION REMOVED FROM THE FIRST ENDS OF SAID HIGHWAYS IN ACCORDANCE WITH THE SELECTION OF A CALLED SUBSCRIBER BY A CALLING SUBSCRIBER; SAID SECOND MULTIPLEX SWITCHING MEANS BEING OPERATIVE ON A TIME SHARING BASIS; MEANS FOR CONNECTING PAIRS OF SAID SUBSCRIBER GROUPS TO A COMMON HIGHWAY THROUGH SELECTED ONES OF SAID FIRST MULTIPLEX SWITCH MEANS WHEREIN A DIFFERNT HIGHWAY IS CONNECTED TO EACH PAIR OF SUBSCRIBER GROUPS AND NO MORE THAN ONE HIGHWAY IS DIRECTLY ASSOCIATED WITH ANY ONE PAIR OF SUBSCRIBER GROUPS SAID SECOND MULTIPLEX SWITCHING MEANS COMPRISING A PLURALITY OF MEANS FOR SELECTIVELY CONNECTING SAID HIGHWAYS ON A TIME-DIVISION BASIS; EACH OF SAID PLURALITY OF MEANS CONNECTED BETWEEN NO MORE THAN TWO OF SAID PLURALITY OF HIGHWAYS. 